FIGS. 17(a) and 17(b) are block diagrams illustrating a data transfer system disclosed in Japanese Published Patent Application No. Hei. 7-64733. In these figures, reference numerals 1-1 to 1-4 designate storage devices, each comprising media, such as an HDD, a CR-ROM, and an optical disk. These storage devices 1-1 to 1-4 constitute a storage device group 2-1. A storage device group controlling unit 3-1 for controlling data readout and the like is connected to the storage device group 21. A buffer memory 4-1 temporarily stores data read out from the storage device group 2-1 by the storage device group controlling unit 3-1. A transfer control unit 5-1 transfers data stored in the buffer memory 4-1 to a terminal connected to the data transfer system through a network. The storage device group 2-1, the storage device group controlling means 3-1, the buffer memory 4-1, and the transfer control means 5-1 constitute a high-speed data transfer unit 6-1. Reference numerals 6-2 to 6-4 designate high-speed data transfer units having the same structure as the high-speed data transfer unit 6-1. Reference numerals 7-1 to 7-n designate terminals connected to the transfer control unit 5-1 to 5-4 of the high-speed data transfer units 6-1 to 6-4.
In the prior art data transfer system so constructed, data is divided into a plurality of blocks each having a prescribed size, for example, 256 K bytes, and is successively stored in the storage device groups 2-1 to 2-4. In the storage device group 2-1, the 256 K byte data block is divided equally into four, i.e., four 64 K byte data blocks, and these data blocks are respectively stored in the storage devices 1-1 to 1-4. Likewise, each of the storage device groups 2-2 to 2-4 stores data of 256 K bytes.
When the terminal 7-1 makes a request for data transfer to the high-speed data transfer units 6-1 to 6-4 and the data requested by the terminal 7-1 are stored in the storage device group 2-1, the storage device group control unit 3-1 reads out the data stored in the storage devices 1-1 to 1-4 and then stores the data in the buffer memory 4-1. Thereafter, the transfer control unit 5-1 transfers the data stored in the buffer memory 4-1 to the terminal 7-1.
When the terminals 7-2 and 7-3 make requests for data transfer, at the same time, to the high-speed data transfer units 6-1 to 6-4 and the data requested by the terminals 7-2 and 7-3 are stored in the storage device group 2-1, the storage device group control unit 3-1 reads out the data requested by the terminals 7-2 and 7-3, which data is stored in the storage devices 1-1 to 1-4, and then stores the data in the buffer memory 4-1. Thereafter, the transfer control unit 5-1 transfers the requested data to the respective terminals 7-2 and 7-3.
In the above-mentioned prior art data transfer system, however, when a plurality of terminals request data transfer at the same time and the data requested by these terminals are stored in the same storage device group, in a high-speed data transfer unit including this storage device group, the storage device group control unit reads out the data requested by the respective terminals from the storage device group and sends the data to the buffer memory, and the transfer control unit transfers the data in the buffer memory to the respective terminals.
Therefore, even though the data transfer system includes a plurality of high-speed data transfer units, when the data requested by those terminals is stored in a storage device group, the load for the data transfer processing is unfavorably concentrated in a high-speed data transfer unit including the storage device group.